Silica composition and production thereof



, 2,943,942 Patented July 5, 1960 SILICA COMPOSITION AND PRODUCTION THEREOF Edward M. Allen, Doylestown, Ohio, assignor to Columbia-Southern Chemical Corporation, Allegheny County, Pa., a corporation of Delaware No Drawing. Filed June 24, 1959, Ser. No. 822,441

8 Claims. (Cl. 106-288) This invention relates to a finely divided alumina-silica pigment which is useful as a reinforcing pigment in rubber compositions and also as a paper pigment, and .to the paper thereby produced.

It is known that desirable rubber products may be prepared by incorporating certain silicates, such as finely divided, precipitated calcium silicate of the proper particle size, into the rubber, and vulcanizing the mixture. Such silicates act as reinforcing pigments which improve the strength and abrasive qualities of the rubber compound. Calcium silicate suitable for this purpose may be prepared by reacting a calcium salt, such as calcium chloride, with an alkali metal silicate, such as sodium silicate, in the manner as disclosed in the United States patent to Muskat and Gage, No. 2,287,700. One difiiculty .with such calcium silicate is that it does not disperse well in rubber. Consequently, the rubber reinforced with this material often is observed to have white specks of undispersed pigment. This makes the product unsightly.

Attempts to produce an aluminum silicate with desirable pigment properties by reacting an aluminum salt with sodium silicate are more diflicult since the aluminum silicate thus precipitated and dried is in the form of a glassy substance. Even when ground up or crushed by usual methods, the product thus obtained is made up of large agglomerate masses which are too coarse and too hard to permit satisfactory use in a rubber compound.

In accordance with this invention, finely divided, white alumina-silica pigment compositions have been prepared, all of which have an average ultimate particle size below 0.5 micron, normally below 0.1 micron. As explained in greater detail below, pigments which are especially valuable in rubber have an average ultimate particle size of 0.01 to 0.05 micron. On the other hand, pigments for paper should be somewhat coarser, usually 0.05 to 0.2 micron or 0.25 micron. This pigment also contains at least 6 moles of SiO per mole of A1 The pigment may be contaminated with portions of calcium sulphate or other alkaline earth metal salt. However, such salt may be substantially absent, if desired. The aluminasilica pigment herein described may be used efieetively as a reinforcing pigment in rubber and as an opacifying pigment in paper.

The pigment herein contemplated may be prepared by several methods. According .to one such method, a water soluble aluminum salt, such as aluminum chloride, is reacted in aqueous medium with a finely divided, precipitated silicate of a metal of group H, series 3 to 8 of the periodic table of elements, such as calcium silicate, having an average ultimate particle size below about one micron, preferably below 0.1 micron.

The composition of the product thus obtained depends upon the nature of the aluminum salt used and also upon the relative proportion of the salt to the calcium silicate or like alkaline earth metal silicate. Where the anion of the aluminum salt forms a water soluble salt with the alkaline earth metal, the calcium or like metal is solubilized in substantially stoichiometric proportions to the aluminum salt added. Thus, Where aluminum chloride is used, the reaction proceeds according to the equation:

where x denotes the initial molecular ratio of Si0 to CaO in the calcium silicate treated.

Normally, the amount of aluminum salt used should be enough to react with substantially all of the calcium silicate or like alkaline earth metal silicate. Thus, the product is largely or preponderantly the alumina-silica composition A1 0 (SiO where y is substantially three times the ratio of moles of Si0 to moles of metal (for example, calcium), in the silicate subjected to treatment. Thus, a pigment is produced in Which the mole ratio of SiO to A1 0 ranges from about 6 to about 40; the molecular ratio of Si0 to all metal oxides being in excess of 2, preferably above 3, and the mole ratio of A1 0 .to the sum of all other metal oxides being above 0.2.

Aluminum salts which will extract calcium and which may thus be used include aluminum chloride, aluminum bromide, aluminum nitrate, aluminum acetate, and the like. Magnesium can be extracted by aluminum sulphate.

According to a further embodiment of the invention, the calcium silicate or like silicate is reacted with an aluminum salt which has an anion which terms a water insoluble salt of the alkaline earth metal, i.e., salts having asolubility below about 2 or 3 grams per liter. In such a case, a mixed pigment containing the aluminasilica pigment described above and the alkaline earth metal salt is produced.

A typical salt of this type is aluminum sulphate. When such a salt is used, the mixture comprises calcium sulphate and the alumina-silica pigment. Where the reaction mixture is relatively dilute, some calcium or even all may be extracted vfrom the pigment due to the fact that calcium sulphate has a small solubility in water. Thus, the alumina-silica pigment may be in an essentially pure state or in admixture with an alkaline earth metal salt such as calcium sulphate. Such salts can be extracted with water.

Since the alumina-silica pigment adsorbs ions, it hequently has adsorbed therein, or in combination therewith, alkali metal or alkaline earth metal ions in amounts which may be greater in mole proportion than A1 0 However, the mole ratio of A1 0 to the sum of all other oxides therein is above 0.2, and the mole ratio of SiO to all metal oxides is above 2, preferably above 3.

When an amount of aluminum salt less than that required to decompose all of the calcium silicate is used, the product contains a very appreciable concentration of calcium, and the amount of CaO therein may be as high or even higher than the A1 0 on a molecular basis.

While the pigment herein contemplated can be produced efiectively using aluminum chloride or aluminum sulphate, other typical water soluble aluminum compounds such as aluminum nitrate, aluminum acetate, aluminum bromide or aluminum lactate, may be used.

The particle size of the aluminum silicate is important. For most uses, this material should have an average ultimate particle size less than one micron, and preferably not substantially in excess of 0.1 micron. Such particles usually are present as fiocs or loosely bound aggregates which can be broken up on milling with rubber.

The exact particle size found desirable depends upon the use to which the pigment is to be put. For rubber uses and maximum reinforcing properties, the pigment should have an average ultimate particle size of 0.01 to 0.05 micron, the best pigments having an average ultimate particle size below 0.04 micron. Such pigments may be in the form of flocs of ultimate particles, some of the flocs being quite large, the preponderant weight of which are in the range of one to fifty microns. The presence of the large flocs normally is not disadvantageous because they are broken up during the milling operation. $1116 requirements of .a=goodvpape r. .pigment armquite i sldifierentlnln such acas theultimateparticlesize. should be above 0.05 micron, preferably in the range-I of. about 0.2. micron.

fi qhe size of-the:=resulting product isdetcrnn'fied to a a material degree by therparticlersize of-thecalcium silicate being treated. Thatzis; theparticlesize of: the pigment tit-whereincontemplated usually:approximatestheparticle of :1 qthewcalcium silicate from which it is produced: @TOI obm tainta pigment:havingthe best pigment rubber reinforcing properties, the aluminum salt-sl1ouldv be -reacted cwith annalkaline-iearth rmetalrsilieat'eihavingt arr 'averagexultimate particle size-below about 0.1: micron -(between 0.01 12010105 micron): as determined by anrelectronmicroscope. :Fon best-rresults; in paper, alarger; calcium'silicatezrangm ing above: 0.05 Emicroir irr.ul'timate tparticle't size used. Precipitation' of: calcium or.-.otherr'alkaline tearthwmetal silicate in-finely divided state; such as is'ihereiir required ixing astream: of;aqueousfcalciunizchlorider{or other chloride: 'of'zianx alkalinei searth. metal): solution with a streanr ofcaqueous: sodium silicateisolutiort underico'ndi- 'tio'nsi which'fsubjectllreflmixture to aihigh: degree of turibulence: and :almost instantaneous: mixingii'. amount off-reactants irr itheirespective streams is proportioned so as. as to 'obtainafcalcium silicate in thedesired concentration .and to .est'ablis'lr an excess of calcium chloride over: the stoichiom'etric=quantityrequired to 'reactwitlrthei silicate. fine efiective way to: produce 1herequired turbulence t is to introduce the =two streams closely together into a central area of a centrifugal' purnpikIii this case,-= the 'agitation'lof the mixture 'is'ieffected asj thetintroduced 'stream's of reactantsfare thrown radially outward bythe pump rotor. V In most cases', it is found desirjableto limit the feed ofi calcium chloride and alkali =-metal silicate solutions entering.-the-pump to=an amount-belowthe -capacity of J- the" pump. For example, ifthe pump is "capable of diseharging -100 g-allons per minute ,':then*'theamount of reacting solutions-appliedtothe'pump islield to at'least 109 percent below, and. usually to -35percent' or-more -below} this' amount."This-appears tof"'afi'ord a-greater 'rl'egree' of-agitatiorr of-the'reaction solutionsand to ensure --pioduction of "a calcium silicatehavingfthe'desired particle-size. "Further, it is-desirable to adjustthe'concentration ofsilicate and calcium chloride in the [solutions so that "calcium silicate will be prep'ared'iniamoncentration approximatelyequal to about 5 to'25'0"grams of'calcium silicate'per-liter of solution or slurry: Moreover; in order to 'ensure'production of a 'calciumsilicate'having' an ex- I tremelysmall particlesize,'-an alkalimtalsilicate having th'e composition 'Nag0(SiO )'wthere x is a number not lessthan '2 nor'more'than 4, is preferablyusedi. "-=results in the production ofacalciumisilicate having the composition-CaO(SiO 'where x is a'num'ber'not'less than 2nor'moretha'n about 5.' However, "other calcium silicates, 'includingmixed' silicates of calcium and other metals such as" sodium; potassium,- arid/or aluminum, -wherex is higher or lowe'r'than'this range, may be used "t'acc'ording to the above described methods if desired.

.Other silicates-which may beluse'd milieu of calcium 'silicate are the corresponding barium,.strontium,.and.magnesium silicatesgiThesei materials: may beprepared by reacting the corresponding metal:chloride-with -sodium j 'fsilicate according to thermethod discussed abovev Moreover,calcium silicate maybe reacted with the correspondingmtahchloride of..these metals-andthe-resulting sili- .i cate. reacted with analuminumusalfas" hereindescribed. According to a furtherflembodiment; ofzrthe invention, ...-.calcium-aluminum--silicate isuitablexfor use as a pigment in the reinforcement ofiu'ubber may-be prepared by-re'acti, a :aaeeaaes or"good"n1bber reinforcement, may bemccomplished by ing an alkali metal silicate with a water soluble aluminum salt in the presenceof a water soluble salt of calcium or similar metal of group 11, series 3 to 8 of the periodic table. Thus, the alumina-silica-calcium silicate pigment 5 may be precipitated directly by mixing a solution of a soluble aluminum salt, such as one of the salts mentioned above, and a water soluble calcium salt, with an aqueous solution" of"- an alkalimetal silicateg such as =-sodium silicate, preferably a silicate in which the SiO- to Na O 10.. moleratio isnotilessithan 2...:JIhe mole ratio. ofncalcium I a r tos'aluminum isaltrinitialb provided I may: be s'aried from about 0.25 to moles of-aluminumpenmole ofscalcium.

., This mixing isleffected underconditions of vigorous agitation; and atypical method of"efiecting*-the"reaction 15 is the one described -above1with:reference to the precipitation of calcium silicate. This process results in formation of the pigment in the desired finely divided state. Typialuminunr-salts which may beuSed-are aluminum chlo- -t -ride, .aluminum:nitrate, aluminum acetate-,zaluminumsul- Q:- phate; andthe.like.. ITypical ca1cium or;rlikel-salts-juseful in this embodiment are calcium,-;magnesium orsbarium chlorides, magnesium. sulphatet orsthe corresponding nifixtr ates.

' vThemol'e ratio 0f A12O-3' toSiO imfthepigment'herein fi-contemplated depends? to a=substantialrdegreegalponx the composition ofthe icalcium:'silicateireatecla ,a'i'hus; in the caset'ofanaluminum s ulphate,-: the: reaction with: calcium silicate isinethewproportion of'wone amol'e-a of aluminum sulphate :perathree moles of calcium: silicate; ETFhUSgr the 0.2Pl'Odl-1Ct produced isapproximately ;Al O (SiO ggiwhere Hencemwhen zcaotsio a is- ;treated-,:=1he";productrrorresponds roughly to the formula; Al 0 9'.9SiO and, in P treatingan: calciumz-xfsilicate having the :Pcomposition oaotsiop zwherex i812 to Settle product corresponds to 'zthe' formula", Al Og(SiQ fiwhere;3x'is 6- toe-15L Byrpretreating: thetrcalciumc silicateiwith hydrochloric acitt onrlike'zacid, it isfipossible'toiincrease thetratio of av'SiOg to CaOrabove Sun In such .:a caseethe products'pmduced'bytreactinglsuch acid-treated.:calciumisilicatefwith anti-aluminum; salt'=Nvi]l2ifOntain-':much=ihigher ratios of a: SiO r toiAl O r-i Moreovenlfi'nelyidividedbilicai precipitiztated in aqueous medium-can be treated= with;aluminum sulphate or-L'like aluminurnsisalt to produce an' a'lum'inaicsepigment. :The aluminai-isilicapigments containing 6 to lfl moles n: of SiO ar'e highly effective paper pigments and have good opacifying-properties in paperl They-are also use- I ful in rubber compositions where-abrasion-resistance is valuable, such as inshoe 'soles.

r lrr accordance' with a: further-"embodiment ofth'e' invention; the pigment which is -p'roduced"may betreated 1 with a: coating agent in orderto imp'rove certain of its properties. -:As an example; the pigmentmay be treated with coatingagentsg s'uch as non-drying' oilsyfor "example, cocoanut oil; corn oil; lard, lard oil, sperm oil or tall'ow, and othen coating-agents, such as olei'c acid, stearic acid, tall oil acids, and similar non-drying "acids; or-th'e alkali l '-metal'or-'ammonium soaps of these acidsFi-The coating agent may be incorporated simply by'forming an aqueous slurry of --the: 'rsulting' pigment" and" adding "the coating -agent-thereto.- "After thegaddition; the' mixture may be agitatetfimlterei-and dried in'the usuahmanner. I

V F Th pigments-'herein--contemplated* having rubber reinforcing properties arei'u'sed to 'reinforcevarious Frubber elastom'ers' or rubber compositions, including natural rubpositions," synthetic "rubber. compositions; .s'uch as P Q- Y n'e copolymers. known a's"GR;S."' b. -'-f be r butadiene 'acrylonitrile polymers, chloroprenelrubm bfif y nzandflike polymers-"of bu't'adiene lj,

; x is theiinitialratio of SiO to:Ca0 in the?caleium ;silicate.

--s sitions produced exhibit superior qualities over those obtained where calcium silicate was used. The amount of such pigment incorporated in these rubber or elastomer compositions generally is about to 100 parts by weight per 100 parts by weight of elastomer or rubber composition.

The invention may be more fully understood by reference to the following examples:

EXAMPLE I An aqueous slurry of finely divided calcium silicate was prepared'by introducing a stream of a solution of aqueous sodium silicate containing 10 grams of SiO as Na O.(SiO per liter of solution and a stream of aqueous calcium chloride containing 10 grams of CaCl:

Sufiicient calcium chloride was used to ensure an excess of at least 10 percent of calcium chloride over the theoretical amount required to react with the sodium silicate. The calcium silicate thus produced had an average ultimate particle size of about 0.03 to 0.05 micron.

This material was washed and thickened and then mixed with an aqueous solution of aluminum chloride in an amount sutficient to provide 20 percent excess aluminum chloride over the stoichiometric amount required to react with all of the CaO in the calcium silicate. The

mixture was held at a temperature of 160 F. for 2 hours.

The excess chloride was then washed out and the remaining material was filtered on Buchner funnels, dried at 220 F., and pulverized. The chemical analysis of the aluminum silicate thus prepared was as follows:

The pulverized material was compounded in GRS rubber, using standard compounding procedures, accordmg to the following recipe:

' Parts by weight G R-S 100.0 Zrnc oxide 5.0 Sulphur 4.0 Santocure 1.75 Picco 100 10.0 -Agerite powder 1.0 Aluminum silicate 82.8

"Santocure N cyclohexyl-Z-benzothiazolsulfonamide. -P1cco 100 Para cumarone-indene resin having a melting point of 7 about 110 to 127 C. Agente powder Phenyl beta-naphthylamine.

EXAMPLE II A stream of an aqueous solution of sodium silicate containing 100 grams of SiO per liter as Na O(SiO and a stream of calcium chloride containing 100 grams per liter of solution were introduced into a centrifugal pump impeller, as described above, while proportioning the calcium chloride so that it remained at least 10 percent in excess. The slurry was washed to removed disper liter into a centrifugal pump, as described above.

solved chloride. Samples of this slurry were reacted with aluminum chloride solution in amounts equal to 10 percent, 30 percent, 50 percent, 75 percent, and percent of the theoretical amount required to react with all of the CaO in the calcium silicate. In these tests, the aluminum chloride was mixed in solution with the slurry and the mixture was allowed to stand for 4 hours at 160 F. The materials thus obtained had the following compositions:

Table 1 Percent by weight Amount of 12. Sample N o. Ignition added perloss cent of (bound S10: A: CaO Stoichioand free metric water) 1 20. 93 58. 92 0. 40 18.03 None 2 25. 75 51. 55 2. 99 17. 72 10 3- 23. 38 57. 43 4. 91 13. 29 30 22. 34 60. 03 5. 63 9. 83 50 22. 26 60. 17 7. 80 9. 08 75 19. 38 64.01 13. 96 2. 44 100 EXAMPLE 111 An aqueous slurry containing 10 pounds of finely divided calcium silicate having an average ultimate particle size of about 0.05 micron, as determined by an electron microscope, and having the composition was thoroughly mixed with 4.44 pounds of aluminum sulphate in an agitating tank. After thorough mixing, the slurry was filtered and dried in a tray-type dryer, at a temperature of 100 to C. The resulting aluminum silicate was a very fine white powder suitable for rubber compounding.

EXAMPLE IV An aqueous slurry containing 100 grams per liter of'finely divided calcium silicate having the composition CaO(SiO was prepared by mixing continuously flowing streams of sodium silicate and calcium chloride, each containing 100 grams per liter of reactant, in a pump as described above. The resulting slurry was titrated with an aqueous solution containing 10 percent by weight of aluminum sulphate to a greenish yellow color using bromothymol blue as the indicator. The pH of such a slurry is about 7. During the titration, the temperature was maintained at 180 F. and the mixture was thoroughly agitated. Thereafter, the resulting product was filtered, washed with hot water, and dried at a temperature of about 100 to 125 C. The dry product was milled. The resulting product was found to be a fine, very white powder which, when dispersed in water, gave a slurry having a pH of about 5.7.

' EXAMPLE V The process of Example IV was repeated except that the titration with aluminum sulphate was efiected at 75 F. The resulting product, when dispersed in water, gave a slurry which had a pH of 7.

EXAMPLE VI A slurry was prepared containing 5 grams of finely divided calcium silicate having the composition and'was dried at 100' to C. to the point where it contained about 5 percent by weight of bound water and about 5 percent by weight of free water, in 95 grams of --water: To this slurry were add'ed'portionso'f ofi molar "aluminum sulphate-'sol-utionand, after eachalddition, the =slurry -was' agitated at 'room temperatnre' for 1 about "minutes; P "Thereupon; the pH- of theslurry" was' rneasured.

According to a further'enibodiment of this invention,

.rthetcal'cium wsilicate may be reacted with an aluminum ,saltsandaan acid. It thelacidTor-msaa watertsoluble'calsalt,;the lprocessl produces'aemixture of silica-and aluminum silicate. l v' Thus, 'Ca'OISiQi); lmaylbev reacted with hydrochloric or'like acid 'to'extract one fourth'to one-half of the calcium therefromand the resulting prod uct reacted with aluminum chloride as described in Exsamples. I andtll, orwvithraluminumsulphata ast., desc1ibed twin Example1H. 'FI'heSe productslhave highernSiQ TAt l A1 0 :moleculan ratios, rangingnas; highaas 7: orabove, depending upomthe amount (of acid .used; Acid-s *whichiformawater; insoluble salts of; the calcium or like metal may be used. Thus, sulphuriczoiisulphurous acids may be added to reactawithzrup to 50 percent of the calcium silicate, and the resulting product treated as in -Bxamplefl, 11, Illtor Alternatively, =the;product ob- =tained--.by. reacting-calcium silicate witlr .310, 30 .011'50 4 .percent a of :the theoretical:- amountaofi aluminumgtchloride, t'astdescribed. in- Example lLimayabe.f1mther-neutralized.tov pH?rwith su1phuric,'=su1phurouslor .likeacids whichiform a water, insoluble calcium ssalt. Productsgproducedaby thismeans comprise of silica-tandaluminum invadmixture 7 with calcium salt ofutheuacid used fortheneutralization.

IIhe above .descripticmi has been directed to fem'bodiments of the invention wherein the .calciumsili- 2 104. Such calcium silicateisaespec'ially' l.usefu1ff0r:-:i production of a 'rubber' pigment according tothisfintven- .tion. 7

explained above,"a pigment having a larger particle size is desired for paper. This can be preparedbytreat- "10 Chloride iso ICOz l, A 1

-As=- shownmbove;= the products maytbaiand fiequetitly a 5 1 iare;mixed:with otherisalts sueh as calcium sulphate and etheilik'e :i'IQuit'e oftenz'they alsopontain other metals such .:as :-calcium;:zine, Ebanium,':and ihe like,' the presence of :whichiare:advantageous in ordento'5maintain the rot-the pigment. They aresinvariably amorphousa a a z'I'hex-vproducts:normally' coritainEZ 10 10 perce1it by weight ofsfreet water (water which ean be kiriven oif by :hatingzatlOSfzCJ fOI- Z l- -hOHIS') and 2 to l09percent by wei'ghthof bomidiwater, i-;e.,':the watenwhichis driventSfE :upon heatingttorLOOO itm2000 C; minus 'the free water. l :I'liezalumina-silica'pimentherein contem ate'cl maf'be used inzspaper was z a J pigment: advantageously in -liu of lztitaniumzdioirid'ei I.ltcis especiallwadvantageoustdpreipi- :taterth;pigmentin situ inthe paper pulp-s'lui' ryr The;.followingiexamples are-illustrative:

LEXAMPLE'WIL v Finely divided calcium silicate slurry prepared as in Example H was reacted with aluminum sulphate solution "tofa'slurrypH'of'4'8. "'I'li'resulting product was filtered parid washedfree of clflori'cleafidthen'diied at Thisproduct'had a surface area of 104 square meters per gram. 7 v l The"re'sulting product was ground tolbieak u iag- 'g'lom'erates 'an'dwas' slurriedin' 'Wat'er'rtb produce afslurry 40 s' p r ntty weight erat aluminum silicate.

ment of calcium silicate of somewhat lower surface areas (5 to square meters per gram) and a larger ultimate gparticle size (greater than 7 0105" micron) "Such silicate may be "produced by a batch process in=which "the 'sodiumsilicate is added toa pool of- -calcium-*chloride solution or vice versa, under conditionssuch that' thel v where y is 6 but less .l than 40,.including fractional ,numbers. The silicates may :contain substantial amounts EBleachedikraft pu'lp was beaten to memes freeness.

- %A portion irof :this pulpr'slurry containin'g percent by weight of pulp (on a dry basis) was 'mixed withthe J'aluminum'silicate slurry in the proportion of 10 parts by weight ofuthealuminumssi-licateper -100 parts-by=weight ;of pulp ,.(dry tbasis)l. sTheamixture-wasthorouglily for 3 minutes andatheresultingslurry-wastreated to sheet, 1 using. a .noble .wood laboratorysheeb machine; *-'Ihej1r;esultinglsheets vwere. tested and compared to similarlypre- ,paredts-heets without.pigment,with the followiug results:

Table III Ashyper, .d aawi "Bright.-

cent by 'percent" nessgperf fiweightg :centl:

Sheets with aluminumsilicateun -Q 16:9, {7min ism Sheets without pigment 013i 1 x 77.0

EXAMPLE VIII A pulpbeatertwashcharged as follows 7 "Unbleached sulphiteipulp 90 Bleached 'lcraftpulp j Hard white env'elope cuttings 90 This charge was dispersed'in--i liters of water and the resulting: slurryewasbeaten in a iNiagaraabeaten for-1 about 80' minutes:.toapproximately- 400 milliliters: freeness,

'70 Canadian standard .(TARBIlstandai-d zczzzmsmif one 1hundredmilliliterslofi preparedirosinloirabout 5 lper cent .Qby weight size-was then-added. Q'I'hereafter, 9 grams 7 of :pregelatinize'd starch was .aaaea the: pulpe as-eimu- *of-metalssother than aluminumyl l gill,e11 having ,latedinthe beater-flonglenoughjto ensure complete mix- 75 -ing. sulphate in the amount are 'percentby the following composition is suitable;

weight, based on the dry weight of pulp, was added as a solution containing 12.92 grams of aluminum sulphate octodecahydrate per liter. At this stage, the pulp consistency was approximately 1.1 percent. Stirring was continued for 2 minutes. Immediately thereafter, the amounts of calcium silicate having the composition CaO(SiO and titanium dioxide indicated in the table were added. The amounts are expressed as percentages of the dry weight of the pulp. Stirring of the mixture was continued for 10 minutes more and the resulting stock was diluted to 8,000 milliliters, divided into ten 800 milliliter portions, and sheeted into paper. The paper was tested for brightness, opacity, bursting strength, weight and thickness, and ash and moisture content,

with the following results:

Table IV Sample Nos 1 2 3 4 6 6 Percent titanium dioxide bywei t 1.0 None 1.6 None None Percent calcium silicate by weight 1.0 2.5 4.0 None 4.0 None Brightness:

Green light 70.8 70.0 72.9 73.2 72.2 70.5 Blue light 61.2 62.2 63.3 63.4 63.1 59.3 Contrast ratio (green light): Reflectance, black backing 66.9 57.0 57.9 57.3 63.0 Reflectance, white backin 79.0 80.1 81.1 80.6 79.7 79.6 Ratio 72.1 71.2 70.3 71.8 71.9 66.6 Contrast ratio (blue light):

Reflectance, black backing 53.7 53.9 64.5 64.9 54.7 49.9 Reflectance, white backing 66.8 67.9 69.3 68.6 68.3 66.9 Ratio 76.2 75.3 74.5 75.9 76.0 70.6 Bursting strength, 1b.]

in. 32.0 34.5 33.0 33.6 350 35.0 Percent ash in oven dry paper 2.23 2.63 2.83 1.86 1.28

Comparison of paper pigmented with the calcium silicate-aluminum sulphate product of this invention (samples 3 and with paper pigmented with titanium dioxide (sample 4) shows that about the same brightness and opacity is imparted by both pigments, and that both papers have about the same bursting strength. Hence, the relatively expensive titanium dioxide may be replaced with a reaction product of this invention at considerable saving in cost and without diminution of physical properties such as strength, brightness or opacity. Titanium dioxide may be used in the present process as in samples 1 and 2.

Although the present invention has been described with reference to the specific details of certain embodiments thereof, such details should not be regarded as limitations upon the scope of the invention except insofar as included in the accompanying claims.

This application is a continuation-in-part of applications Serial No. 806,212, filed April 14, 1959, and Serial No. 616,595, filed October 18, 1956, now abandoned, which application was a continuation-in-part of applications Serial No. 770,169, filed August 22, 1947; Serial No. 277,760, filed March 21, 1952, now abandoned; Serial No. 283,721, filed April 22, 1952, now United States Letters Patent 2,805,955; Serial No. 355,865, filed May 18, 1953, now United States Letters Patent 2,786,777;

10 and Serial No. 473,057, filed December 3, 1954, now United States Letters Patent 2,786,776.

I claim:

1. Finely divided, precipitated, White alumina-silica pigment in the form of flocs of ultimate particles and having at least 6 but less than 40 moles of SiO per mole of Al O said pigment having an average ultimate particle size below 0.1 micron and containing up to but not in excess of 10 percent by Weight of free water.

2. Finely divided, precipitated, white alumina-silica pigment in the form of flocs of ultimate particles and having at least 6 but less than 40 moles of SiO; per mole of A1 0 said pigment having an average ultimate particle size of 0.01 to 0.05 micron and containing up to but not in excess of 10 percent by weight of free water.

3. Finely divided, precipitated, white alumina-silica pigment in the form of flocs of ultimate particles and having at least 6 but less than 40 moles of SiO;, per mole of A1 0 said pigment having an average ultimate particle size of 0.05 to 0.1 micron.

4. Finely divided, amorphous alumina-silica pigment in the form of fiocs of ultimate particles and having at least 6 but less than 40 moles of SiO; per mole of A1 0 the mole ratio of Si0 to all metal oxides in the pigment being in excess of 2 and the mole ratio of A1 0 to the sum of the other metal oxides being above 0.2; said pigment having an average ultimate particle size of 0.01 to 0.05 micron and containing up to but not in excess of 10 percent by weight of free water.

5. Finely divided, white alumina-silica pigment in the form of flocs of ultimate particles and having at least 6 but less than 40 moles of SiO; per mole of A1 0 said pigment having an average ultimate particle size below 0.1 micron.

6. Finely divided, precipitated, white alumina-silica pigment in the form of flocs of ultimate particles and having 6 to 15 moles of SiO;; per mole of A1 0 said pigment having an average ultimate particle size below 0.1 micron.

7. Finely divided, amorphous, precipitated aluminasilica pigment in the form of flocs of ultimate particles and having 6 to 15 moles of SiO per mole of Al O the mole ratio of SiO to all metal oxides in the pigment being in the excess of 2 and the mole ratio of A1 0 to the sum of the other metal oxides being above 0.2, said pigment having an average ultimate particle size of less than 0.1 micron.

8. Finely divided, precipitated, white alumina-silica pigment in the form of flocs of ultimate particles and having 6 to 15 moles of SiO;, per mole of A1 0 said pigment having an average ultimate particle size of 0.01 to 0.05 micron and containing up to but not in excess of 10 percent by weight of free water.

References Cited in the file of this patent UNITED STATES PATENTS 2,739,073 Bertorelli Mar. 20, 1956 2,848,346 Bertorelli Aug. 19, 1958 FOREIGN PATENTS 805,494 Great Britain Dec. 10, 1958 571,163 Canada Feb. 24, 1959 

1. FINELY DIVIDED, PRECIPITATED, WHITE ALUMINA-SILICA PIGMENT IN THE FORM OF FLOCS OF ULTIMATE PARTICLES AND HAVING AT LEAST 6 BUT LESS THAN 40 MOLES OF SIO2 PER MOLE OF AL2O3, SAID PIGMENT HAVING AN AVERAGE ULTIMATE PARTICLE SIZE BELOW 3.1 MICRON AND CONTAINING UP TO BUT NOT IN EXCESS OF 10 PERCENT BY WEIGHT OF FREE WATER. 